UCLA Integrated Substance Abuse Programs (ISAP) is resubmitting an application requesting R03 funding to conduct secondary analyses focusing on mental health (MH) data collected in a previous project. A statewide policy change in the adjudication of offenders with substance use disorders (SUD) occurred in California with the Substance Abuse and Crime Prevention Act of 2000 (SACPA). Data collected through SACPA afford researchers the opportunity to assess MH and SUD issues in the largest probation and parole populations in the nation. Intervention planning and services implementation for offenders are hindered by significant gaps in our knowledge about MH and SUD co-morbidity, utilization of MH services, and related social services utilization and costs. ISAP accumulated data from state and county sources to conduct an evaluation of the 'pipeline'flow of SUD offenders into alcohol and drug treatment under SACPA and of the related cost effects on criminal justice and social services related to SACPA implementation. The proposed work will capitalize on these data, collected on three one-year SUD offender cohorts (one year before and two years after SACPA initiation), by examining variation of MH diagnoses and utilization of MH services according to age, gender, ethnicity, primary drug of abuse, MH diagnosis, and other variables. We will examine differences between those with and without MH diagnoses in offender characteristics, service utilization patterns, and costs, especially as they relate to outcomes of MH and substance abuse treatment. The availability of Addiction Severity Index (ASI) data for that subsample entering alcohol or drug treatment allows for analyses to assess the extent of convergence or divergence in results from the official and self-report data sources and to use Addiction Severity and Psychiatric Severity scores as additional variables of interest. The impact of mental illness on utilization of other social services will be examined, supporting an assessment of government-incurred costs related to MH disorders among SUD offenders. Findings will inform potential policy and practice improvements.